A type of device and a type of process for manufacturing hollow plastic objects are known in practice. It is customary, especially in the manufacture of plastic bottles, particularly PET bottles, to convey so-called preforms made of plastic from a repository to a molding station. This molding station may include, for example, a heating device in which preforms are heated to the temperature needed for the subsequent stretch blowing process. The final shape of the bottle is then created during the subsequent stretch blowing process.
However, a defectively manufactured preform can cause operating problems if it reaches the heating device and/or the stretch blowing device. For example, damage to the mouth area of a preform may result in leakage during the stretch blowing process. Consequently the preforms are moved past an inspection station in the shape of a mandrel wheel. The individual mandrels of this wheel penetrate the mouth of a preform and scan it mechanically so as to be able to detect certain defects in the mouth area. If a defect is detected, the machine is stopped and an operator must remove the defective preform. Consequently, an operator must be present and the machinery may be subject to downtimes that reduce its output. In addition, there is a risk that the penetrating action of the mandrel wheel may damage the plastic preforms.